In an image forming apparatus that forms an image on a recording medium, a liquid ejection head includes a plurality of discharge orifices that eject liquid, such as ink, as droplets. The droplets ejected from the discharge orifices of the liquid ejection head are each formed of a main drop portion formed in a spherical shape at the distal end of the droplet and a liquid column (tail) following the main drop portion. The liquid column is separated from the main drop portion, and the liquid column itself is divided to form a subdrop portion (satellites). To form an image on a recording medium, it is preferable that the number of satellites be small because the satellites cause displacement of landing positions. PTL 1 discloses a liquid ejection head having a structure in which protrusions are provided at the edge of a discharge orifice to reduce the number of satellites of the droplets.
The protrusions at the discharge orifice of the liquid ejection head protrude toward the center of the interior of the discharge orifice in a direction parallel to the scanning direction of the liquid ejection head. Providing the pair of protrusions at the discharge orifice so as to protrude toward the center of the interior of the discharge orifice makes it easy to separate ejected ink droplets and remaining ink from each other. Furthermore, a resistance difference caused in the discharge orifice by the pair of protrusions can shorten the tail, thereby reducing the number of satellites.
The liquid ejection head adopts a thermal system that heats ink and ejects it as droplets. The liquid ejection head includes heaters for heating ink and pressure chambers accommodating the heaters and has discharge orifices on the heaters in such a manner that the centers coincide with the centers of the individual heaters. To form the discharge orifices, the pressure chambers, and so on of the liquid ejection head, photolithography for obtaining a desired shape by exposure and development is used.
However, according to the invention disclosed in PTL 1, the correlation between the discharge orifices and the exposure positions of the pressure chambers can be deviated during manufacture by photolithography due to variations in processing accuracy in the manufacturing process. If the discharge orifice is formed in a offset position in a direction perpendicular to the protruding direction of the protrusions of the discharge orifice due to the deviation, the interval between the edge of the discharge orifice and the wall of the pressure chamber becomes extremely small because the pressure chamber is smaller than the discharge orifice in plan view. When ink is ejected through the thus-configured discharge orifice, the tails of ink droplets during ejection bend from the center of the discharge orifice in a direction in which the edge of the discharge orifice and the wall of the pressure chamber are in close contact since the center of the discharge orifice and the center of the pressure chamber differ in plan view. The bending of the tails causes the main drops and the satellites to land at positions out of target landing positions on the recording medium, thus posing the problem of degrading the image quality of the recording medium.